Although the rules state the GM can do these things, the real question is here is "When should this happen, and how should it happen in a way that is fun, and not un-fun?"
Based on your "GM's shouldn't be gods" comment, my guess is your equipment was stolen, destroyed, or teleported away without a chance to do a saving throw, take action, skill check, or anything, right?
I'm going to point out a very basic game design idea that shows up in more of the modern game design:
When the GM wants to do something negative to the player characters, the players should always get a chance to DO SOMETHING to avoid or deal with it.
Games like Burning Wheel and Apocalypse World are built on this idea of heroic fiction is about protagonists facing consequences - but their protagonism is based in the fact they potentially can overcome the dangers and troubles. When you take that away, not only is it unfun from a story standpoint, it's unfun from a game standpoint - games are built on some element of choice.
Anyway, the answer you're looking for isn't about pointing to a rule in the book and saying "You can't do that", it's going to be talking as a group:
"Hey, let's pause the game. This thing that happened is unfun and unfair because you've taken important abilities away from our characters without any forewarning or chance for us to do anything about it. It feels like getting stuck in a cutscene in a videogame. What's the problem you're trying to solve, and is this the best way of doing it?"
Mind you, that's the discussion to have if your GM is simply at a loss of how to fix something in their game. The unfortunate fact is that most of the time when you have this kind of thing in gaming, it's less "Well, I did what the book told me" and more "I wanted to assert authority" "The players are doing something wrong but instead of talking it out I'll punish their characters" and a lot of other weird passive aggressive things.
You've played with the GM for a year - do they do these kinds of "taking away your choices" things often? That's going to be the easy indicator of whether you should keep playing or just find a new group.